1. Field of the Invention
The present invention relates to a method for measuring the speed of movement of a beam spot during track movement of the beam spot in an optical memory apparatus for large-scale computers, personal computers, and the like.
2. Description of the Related Art
An optical disk apparatus performs reading (reproduction) and writing (recording) with respect to an optical disk, rotated about a rotary shaft by a motor, by an optical head at a desired track by moving the optical head in the radial direction of the optical disk by a head drive motor.
The speed of movement of the optical head drive motor is controlled by how many tracks a beam spot is moved per unit time. That is, the amount of track movement of the optical beam spot per unit time is measured and the speed of movement of the optical beam spot with respect to the tracks is found from the amount of track movement. Next, the difference between the target speed predetermined in accordance with the remaining amount of tracks until the track to be accessed and the speed of movement is used as the speed error, the design deceleration model current, is added, and the current of the optical head drive motor is controlled.
During high speeds, the resolution is just right. However, at low speeds, the resolution with respect to a track is completely insufficient, so the speed cannot be measured in the same way as in high speeds.